Applying nitrocellulose varnishes



o sures and blistering and are likely to come off or they present otherphysical disadvan-' Patented Nov. 4, 1930 UNITED STA TEs PATENT OFFICAPPLYING NITROCELLULOSE VARNISHES No Drawing. Application filed November30, 1926, Serial 'No. 151,827, and in Germany December 4, 1 925.;

This invention has reference to improvements in varnish coatings ofnitrocellulose and the like, and it is intended to devise means ofproducing a better adhesion of the 6 nitrocellulose coating to thearticle to be treated than it was possible to obtain by the meansheretofore suggested. The invention has also for its object to generallyimprove,

the process of manufacture of such varnishes and varnish coats, as wellas the quality of such products. Other objects and advantages willappear from the specification and claims.-

For the purpose of coating articles with varnishes or lacquers, such asfor instance in the case of the coating of automobiles and othervehicles and the like, oil varnishes have been employed almostexclusively until recently. The long duration of the drying required forsuch varnishes was, however, a serious drawback which has becomeparticularly annoying with the introduction of the so-calledseries-method of manufacture of automobiles and the like, so that itbecame necessary to devise means of substituting a suitable, but morerapidly drying product for the oil varnishes heretofore employed. Asapartial substitute for oil varnishes it has been suggested to make useof cellulose-ester varnishes. While these varnishes and lacquers dryvery quickly, there is the inconvene ience that such varnishes fail topossess sufiicient body, inasmuch as the celluloseestercan only bedissolved in the solvents employed at very low concentrations. Such thinvarnishes or lacquers will accordingly requiremore successive coats,which will to a large extent compensate the advantage of more rapiddryin thereof. Besides, such varnishes are lia le to showfistageousfeatures, and there is the additional difficulty that such methods arerather expensive by the great amounts of valuable solvents required.

The nitro-cellulose-varnishes and lacquers have become important, sinceit has become possible to manufacture nitro-cellulose yieldingcomparatively thinly liquid solutions by means of which varnishes orlacquers with about 20 to 40 percent solids can be obtained that can beapplied in jets or by sprinkling. To this class of varnishes belongs forinstance the Du-Pont-Errtee-Duco-Finish. These Duco-varnishes show thedrawback, however, that they do not adhere directly to sheet metalsurfaces, so that it becomes necessary to provide for grounding thesurfaces twice with oil paint. This previous grounding of I the surfacerequires at least two days, particularly in cases where stopping orfilling is necessary; and there is also the inconvenience that theseDuco-varnishes produce a dull surface, which is objectionable inmanycases.

, Now this invention'is adapted to overcome all these drawbacks anddisadvantages resulting in the application of coats ofnitrocellulose-varnishes. It has been ascertained in the course of myexperiments that the intermediate layer intended to secure such coats ofcelluloid-like nature to the underlying surface, instead of consistingof. a grounding of oil-paint or varnish, may comprise a suitablycompounded solution of nitro-cellulose; and by this means a very quickcompletion of the entire coating process with the simultaneous reliablefixing of the coat to the surface of wood, sheet metal or the like ismade possible. In accordance with this invention it has been foundadvantageous to employ intermediate layers of nitro-cellulose possessinga solubility which is different from the other coats. These difi'erentsolubilities do not refer to the slight variations of solubilityexhibited by the ordinary collodion-cotton with a content of nitrogenfrom, say 10.5% to 12.5%, but the invention refers particularly to thedifferent solubilities of the kinds of nitrot-cellulose containing morethan 12.6% of nitrogen, the so-called gun-cottons, the solubility ofwhich in etheralcohol is less than that of the ordinarycollodion-cotton. A grounding coat composed of this kind ofnitro-cellulose-solutions will so as not to produce any dissolvingaction upon the fastening intermediate layer. This varnish or lacquerobtained from the kinds of "nitro-cellulose above specified havingmorethan 12.6% of nitrogen may be compounded in the usual manner withsoftening agents, coloring pigments, natural and artificial resins-andvarnishes. This grounding varnish may moreover be employed as a ploymodifications of nitro-cellulose with different solubilities and varyingcontents of nitrogen with advantage, by which means the durability ofthe entire coating of varnish is greatly increased. Hence, the entiremethod of the application of varnishesin accordance with this inventiontherefore comprises for instance the applying of a'suitable solution ofgun-cotton nitrocellulose as the ground, then the application of thecoating varnish of any desirable adjustable hardness, and theapplication of the gloss-varnish by sprinkling orby jets; Each of thesethree varnish layers containing easily volatile solvents dries veryrapidly, about one to two hours drying being generally suificient forevery varnishing and painting operation at 25 Centigrade up to therubbing and burnishing of the coatings.

.A numerical example may explain still more clearly the method oftheinvention. To an iron sheet there is applied by means of t a brush orotherwise a primary grounding layer by using a lacquer of the followingcomposition:

10% low-viscous nitrocellulose of 12.8% N., 5% rosin-ester, 8%butylphtalate, 20% butyl-acetate, 17% propyI-acetate, 15%

ethyl-acetate, 15% propanol, 10% pigment."

-After the drying of this grounding coat a second layer. of varnish isapplied which may becom'posed of the following constituents:

13% low-viscous nitrocellulose of 12% N.,

7% butylphtalate, 10% butanol, 35% methand, 25% toluol, 4% castor oil,6% pigment,

It should, of course, be understood that the n vention is susceptibleofmodifications, and that no limitations on the invention are intent anda lower ether-alcohol solubility than the nitrocelluloses used in thesubsequent coating solutions.

. 2. In a method of applying coatings of nitrocellulose varnishes uponbases with the aid of a primary binding layer, the applying as primarybinding layer, of a nitrocellulose solution comprising a nitrocellulosehaving a substantially higher nitrogen content and a lower ether-alcoholsolubility than 5 the. nitrocelluloses used in the subsequent coatingsolutions, and the employing for these subsequent coatings, ofnitrocelluloses which differ considerably amongst them selves in respectof solubility and nitrogen content.

3. In a method of applying coatings of nitrocellulose varnishes tosurfaces with the a1d of a primary binding layer, the employment asprimary binding layer, of a guncotton-nitrocellu-lose having a nitrogencontent above 12.6% and incomplete ether-alcohol solubility, and theemployment for the further coatings, of nitrocelluloses differingconsiderably amongst themselves in respect of solubility and nitrogencontent.

4. In a method of applying coats of nitrocellulose varnishes to surfacesof work with the aid of a primary bindinglayer, the using for theprimary binding layer, of a nitrocellulose having a nitrogen contentabove 12.6%, and for the following layers, of nitrocelluloses havinganother nitrogen content than the nitrocellulose of the primary coatinIn a method for producing superimposed layers of nitrocellulosevarnishes differing from one another in content of nitrogen and degreeof ether-alcohol solubility using as nitrocellulose of the groundinglayer a nitrocellulose of a substantially higher nitrogen content and alower ether-alcohol solubility than the nitrocelluloses of thesubsequent coatings.

- 6. In a method for producing superimposed layers of nitrocellulosevarnishes, constituting the grounding layer by a nitrocel-' .lulosehaving a nitrogen content above 12.6%

and an incomplete ether-alcohol solubility,

whilst the other layers have another nitrogen content than thenitrocellulose of the groundlayer.

In testimony whereof I afiix my signature.

HANS F. SOHULZ.

tended other than those imposed by the scope

